HMOs have become the subject of much interest in recent years due to their roles in numerous biological processes occurring in the human organism. Mammalian milk contains at least 130 of these complex oligosaccharides (Urashima et al: Milk Oligosaccharides, Nova Biomedical Books, New York, 2011, ISBN: 978-1-61122-831-1).
Previously, the only source of HMOs had been mammalian milk which contains mostly water, together with 55-70 g/l lactose, 24-59 g/l lipids, ca. 13 g/l proteins, 5-15 g/l HMOs and ca. 1.5 g/l minerals.
However, efforts to develop processes for synthesizing these oligosaccharides have increased significantly in the last ten years due to their roles in numerous human biological processes. In this regard, processes have been developed for producing HMOs by microbial fermentations, enzymatic processes, chemical syntheses, or combinations of these technologies. For example, by chemical processes, LNnT can be made as described in WO 2011/100980 and WO 2013/044928, LNT can be synthesized as described in WO 2012/155916 and WO 2013/044928, a mixture of LNT and LNnT can be made as described in WO 2013/091660, 2′-FL can be made as described in WO 2010/115934 and WO 2010/115935, 3-FL can be made as described in WO 2013/139344, and 6′-SL and salts thereof can be made as described in WO 2010/100979. As examples of biotechnological processes, WO 01/04341 and WO 2007/101862 describe how to make core human milk oligosaccharides optionally substituted by fucose or sialic acid using genetically modified E. coli. As an example of enzymatic processes, sialylated oligosaccharides can be made as described in EP-A-577580.
Efforts have also been made to develop processes for synthesizing enzymatically mixtures of HMO oligosaccharides, without having to synthesize all of the component oligosaccharides of the mixture as described in WO 2012/156897 and WO 2012/156898. Such processes have provided reaction mixtures containing a plurality of different oligosaccharides.
However, better processes have been sought for the synthesis of mixtures of HMOs, especially mixtures consisting of three HMOs, particularly 6′-SL, LNnT and LST c.
Evidence is accumulating that the resident community of microbes, called the microbiome, in the human digestive tract plays a major role in health and disease. When the normal composition of the microbiome is thrown off balance, the human host can suffer consequences. Recent research has implicated microbiome imbalances in disorders as diverse as cancer, obesity, inflammatory bowel disease, psoriasis, asthma, and possibly even autism. HMOs are believed to positively modulate the microbiome, and they are of increasing interest for this purpose. However, the remarkable diversity of HMOs, coupled with their lack of availability, has hampered studies of the specific functions of individual HMOs. There is a clear need for specific HMOs or combinations of HMOs to modulate the microbiome in a desired manner, so as to address specific human health issues.